Expanding plug or mandrel



March 13, 1934. J, J, DUNN I 1 ,951,087

EXPANDING PLUG OR MANDREL Filed June 19, 1930 Patented Mar. 13, 1934 t EXPANDING PLUG on MANDREL I Jerry Jay Dunn, Ellwood City, Pa., assignor to National Tube Company, a corporation of New Jersey Application June 19, 1930, Serial No. 462,292

2 Claims. (Cl. 78-103) This invention relates to mandrels for use in to impart to the tube or billet a rotary motion the manufacture of seamless metal tubes and and a motion of translation along its axis of has in view the provision of a device of this rotation. class'by means of which the quality or the re- The improved mandrel or expanding point is 5 sultant product is improved and the life of the particularly adapted for tubes of a size requirmandrel prolonged. ing more than one piercing operation. The

Generally speaking, the improvement consists mandrel or head is supported against endwise in dividing the mandrel into a plurality of secmovement by a bar 6, said bar being provided tions or parts which when assembled, form a with an enlarged annular portion 6 formed with 10 -unit having a smooth, unbroken, gradually eX- a bearing surface and a conical shaped boss or panding surface contour, the sections being free cylindrical projection 7, the latter serving to cento rotate relatively to one another about the ter the mandrel or head and maintain it in axial common axis 0 the mandrel, thus permitting alinement with the supporting bar 6. The maneach section to agate at the speed of rotation drel or head assembly is shown partly in section 15 of the interior sur ce of the material or partlyand comprises a point end 8 formed with a cyformed tube in contact therewith, thereby reduclindrical projection or boss 9 which fits into a ing frictional wear on the mandrel and surface part 10 and maintains the end 8 in alinement and internal strains and stresses on the tube unwith the mandrel as a whole, the parts 8 and 10 dergoing the cross-rolling process. being free to rotate independently of each other.

20 Heretofore mandrels comprising independently The part 10 is that portion of the mandrel or rotatable parts, each part being substantially head which performs the major portion of the similar to a one-piece mandrel, have been propiercing operation and consequently bears the posed. In such structures, each .'part has been brunt of the endwise thrust imposed on the given a conical or conoidal shape and cooperates mandrel. The better to resist this thrust, the

5 with a similarly shaped surface'portion of the part 10 is provided witharecessed cylindrical pro- 0 rolls, the tube being first fed over the piercing jection 12 which is directly attached to the suppoint, which is in effect a one-piece mandrel porting bar 6, the recess in the said projection in itself, then converging around a necked porreceiving the boss 7 formed on the end of the tion of the mandrel and then expanding over the bar. By this means, the endwise thrust imposed 30 next part. It has been found; however, that on the part 10 is communicated directly to the such constructions are impractical and do not supporting bar 6, the part 10 rotating at the function as contemplated, the same frictional same angular velocity as the said bar. wear being present in such instances as in a one- The parts of the mandrel or head assembly piece mandrel as commonly used. which are shown in section and indicated at 13 The advantages of the improved mandrel will and 13 function to smooth the inside of the tube no become apparent in view of the following deand guide the latter as it becomes less and less scription taken in conjunction with the drawing, elliptical in cross-sectional contour. ,These parts wherein: may if desired be formed in one piece and are Figure 1 is a view in; section and elevation bored to fit over the cylindrical portion 12 and 40 of a mandrel constructed in accordance with the rotate freely thereon. The part 13 bears against features of the invention, together with a set of the bearing surface of the enlargement 6 of the rolls and a billet or partly formed tube undersupporting bar 6. going the cross-rolling operation. In operation, the heated billet is pushed into Figures 2 and 3 are views in section taken on contact with the surfaces of the rolls 5, which 45 the lines II--II and III-IIL respectively, of are rotated and advance the rotating billet in Figure 1. an axial direction, bringing it into contact with The reference numeral 5 designates a pair of the point 8 of the mandrel assembly. rolls, which rotate on axes which do not inter- The point 8 then starts to rotate in unison sect. The axes are-so located with reference to with the material, which continues to advance so each other that by giving the proper shape to and flows over the point, coming into contact the rolls a pass is formed therebetween which with'the part 10, the latter in turn then starting first converges in the direction of travel of the to rotate in unison with the rotating billet. The billet or partly formed tube, indicated at 'T, and angular velocity or speed of rotation of-the part then diverges. The axes of the rolls and pass 10, however, is of a different ratio than the an- 55 are so located that the rotation of the'rolls tends gular velocity of the point 8', due to the increase in cross-sectional diameter of the then oval tube T, note Fig. 2. i

As the billet or partly-formed tube continues to advance, it reaches the parts 13, and 13 rolling action. A portion of the reduction takes place in an axial direction but the major portion is in a circumferential direction and causes an increase in diameter. Further advance brings the billet into the diverging part of the pass, and thereafter the ovality of the partlyformed tube is gradually reduced, until as the tube .passes out of contact with the rolls, it" is circular in cross-section. It is apparent that the rolls tend to impart different angular velocities to different sections of the material in the pass. This tendency is resisted by the cohesion of the particles of the material to the extent that, roughly speaking, all sections rotate at the same angular velocity.

It is also apparent that at any cross-sectional point, the mandrel tends to rotate at the same surface speed as that of the inside surface of the tube at that point; The perimeter of the inside surface of the tube section is greater than that of the corresponding section of the mandrel, the

ratio between these two quantities varying, being much less at some sections than at others. As the tube rotates at a constant velocity, it follows from this variable ratio that the tube tends to cause the mandrel to rotate at different angular velocities at different sections.

If, therefore, the mandrel is formed in one piece, it can have at any one time only one rate of angular speed, and hence the tube at each respective section except one will slide over the surface of the material, retarding flow of the material being worked and causing wear on the meme? mandrel. This action also exerts stresses on the material during formation of the tube which have a detrimental effect on the quality of the result- ;ant product.

By making the mandrel of several parts or sections which are free to rotate relatively to each other, the friction generated between the interior surface of the partly-formed tube and the surface of the mandrel in contact therewith is reduced to a minimum, with the result that the quality of the tube is improved by the avoidance of needles stresses in its formation and the life of the mandrel is prolonged, which in turn affects the quality of the tube, as the best form of mandrel is maintained in service over longer periods of operation.

The herein described type of mandrel may also be used for expanding and. smoothing with the same advantageous results. It will also be obvious that suitable bearings or bearing material may be used between the various rotating parts and that various modifications in structure may be adopted without departing from the scope of the invention.

What is claimed as new is:

1. A mandrel of the class specified,'comprising, in combination, a rotatable supporting bar provided with a cylindrical projection, a frustoconical piercing extremity formed in sections having relative rotation, one of which is formed with a recessed cylindrical projection adapted to receive the projection on the supporting bar, and an annular independently rotatable body section mounted on and encircling the cylindrical projection of the said piercing extremity section.

2. A mandrel of the class specified,-comprising a rotatable supporting bar formed with a 

